Method for preparing ellagic acid by photocatalytic tannin

Abstract

The invention provides a method for preparing ellagic acid from photocatalytic tannin, which is to use plant tannin as raw material, dissolve it in an aqueous solution, add mpg-C3N4 photocatalyst, and perform photocatalytic degradation reaction at a certain temperature; add acid to the reaction solution to adjust the pH value, filter, wash the filter cake, and dry to obtain a crude ellagic acid product; the crude product is refined and purified by alkali dissolution, activated carbon decolorization filtration, and dilute acid reduction precipitation to obtain ellagic acid with a content of ≥98%wt. The preparation method is simple in process and the prepared product has high purity.

Description

Technical Field

[0001] The invention belongs to the field of fine processing of plant tannins, and particularly relates to a method for preparing ellagic acid by using photocatalytic tannins. Background Art

[0002] Ellagic acid, also known as hexahydroxybiphenyl diolate, has multiple physiological activities, including antioxidant, anti-cancer / anti-mutagenic properties, and inhibition of human immunodeficiency virus. It is widely used in the fields of medicine, cosmetics, and health food raw materials.

[0003] CN105524074A discloses a method for preparing ellagic acid by alkaline hydrolysis of tannin, which uses tannin as a raw material, adds an alkaline catalyst, and performs an ultrasonic-assisted hydrolysis reaction at a certain temperature to prepare ellagic acid. The production process of this method will produce a large amount of strong acid, strong base and high-concentration salt, forming wastewater that is difficult to treat. Summary of the invention

[0004] The invention provides a method for preparing ellagic acid by photocatalytic tannin, which has simple process, high product purity, better environmental protection and good economic benefits.

[0005] The technical solution of the present invention is a method for preparing ellagic acid by photocatalytic tannin, comprising the following steps:

[0006] S1, dissolving tannin in water, then adding a photocatalyst to carry out a photocatalytic degradation reaction, adding acid to carry out acidification precipitation after the reaction is completed, filtering, washing and drying the filter cake to obtain a crude ellagic acid product;

[0007] S2. The crude product is dissolved with alkali, then decolorized, and then acid is added to reduce the precipitate, which is filtered, washed, and dried to obtain the ellagic acid product.

[0008] Furthermore, the tannin is oak tannin and / or caraway tannin.

[0009] Furthermore, the mass ratio of the tannin to water is 1:10-40.

[0010] Furthermore, the photocatalyst is mpg-C3N4, and its added amount is 10-20% of the mass of tannin.

[0011] Furthermore, the reaction temperature in S1 is 60-100° C., and the reaction time is 0.5-1.5 h.

[0012] Furthermore, the acid added in S1 is a hydrochloric acid solution, and the pH is adjusted to below 6.

[0013] Further, the crude product in S2 is dissolved with a sodium hydroxide solution, activated carbon is added for decolorization, and then the activated carbon is removed.

[0014] Furthermore, the acid in S2 is a hydrochloric acid solution, and the pH is adjusted to below 4.

[0015] The invention also relates to the use of mpg-C3N4 as a photocatalyst in extracting plant tannins to prepare ellagic acid.

[0016] The present invention has the following beneficial effects:

[0017] The present invention uses mpg-C3N4 photocatalyst as a catalyst for degrading plant tannins to generate ellagic acid. The reaction conditions are simple, the catalyst and acid-base reagents used are low in price, the reaction time is short, and environmental pollution can be controlled while overcoming the shortcomings of complicated preparation operations and long production cycles. The obtained product has high purity and is suitable for production and promotion.

[0018] The wastewater generated by this technology mainly comes from the hydrolysis and separation stage, and the wastewater generated in the refining stage can be applied to the reaction stage. Compared with the alkali catalyst method, the wastewater volume is reduced by more than 60%, and the wastewater pollutants and salt content indicators are greatly reduced. Conventional wastewater biochemical methods can be effectively treated.

[0019] Carbon nitride (g-C3N4) material is a new type of non-silicon-based carbonaceous material with a unique two-dimensional electronic structure, good physical and chemical stability, thermal stability, low density and good wear resistance. As a new type of photocatalyst, mpg-C3N4 has the advantages of stable chemical properties, high temperature resistance, and suitable energy band structure. Due to the unique structural characteristics of mpg-C3N4, more active sites are exposed on the surface of the material, and its rich pore structure is more conducive to mass transfer and diffusion in multiphase reactions, so that mpg-C3N4 shows higher performance in many application fields. The inventors have found that most of the existing photocatalysts have low catalytic degradation efficiency for tannins, while mpg-C3N4 photocatalysts have a selective catalytic cleavage effect on galloyl. The present invention uses the photocatalyst mpg-C3N4 to photocatalytically degrade tannins to prepare small molecule polyphenol ellagic acid. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The figure is a flow chart of the method of the present invention.

[0021] Figure 2 It is the HPLC chromatogram of the product obtained in Example 2.

[0022] Figure 3 This is the 1H-NMR spectrum of the ellagic acid product obtained in Example 2.

[0023] Figure 4 This is the 13C-NMR spectrum of the ellagic acid product obtained in Example 2. DETAILED DESCRIPTION

[0024] The embodiments of the present invention will be described in detail below with reference to examples, but those skilled in the art will appreciate that the following examples are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention.

[0025] Example 1 Preparation of caraway tannin

[0026] The esculenta caryophyllus is crushed and heated and extracted with water as a solvent. The extraction method can be conventional immersion, microwave-assisted extraction, and ultrasonic-assisted extraction. The extraction times are 1-3 times, and the extraction time of each time is 1-3 hours. The residue is filtered out, and the esculenta caryophyllus tannin is concentrated by vacuum heating and dried to obtain the esculenta caryophyllus tannin. The esculenta caryophyllus tannin used in the present invention has a content of 70wt%.

[0027] Example 2

[0028] The method for preparing ellagic acid by using tannin of physalis, comprises the following specific steps:

[0029] (1) Hydrolysis: Take 5 g of caryophyllaceous tannin, dissolve it in 100 mL of warm water, add 0.5 g of mpg-C3N4 photocatalyst (the mpg-C3N4 photocatalyst in this case is provided by the Chinese Academy of Forestry, and can also be purchased from the market), and stir the reaction at 100 °C for 1 h.

[0030] (2) Acidification separation: Add dilute hydrochloric acid to the reaction solution while stirring until the pH value of the reaction solution reaches 6, filter, wash the filter cake with water, and dry to obtain 1.57 g of crude ellagic acid product, the purity of which is 79.8% as determined by HPLC, with a yield of 31.4%.

[0031] (3) Refining and purification: The crude ellagic acid product is added to a sodium hydroxide solution and activated carbon, and reacted at 50°C for 1 hour. The reaction solution is filtered, and the filter cake is washed with water. The filtrate and the washing liquid are combined. Dilute hydrochloric acid is added dropwise to adjust the pH value of the solution to 4, and the light yellow ellagic acid refined product is obtained by filtering.

[0032] (4) Drying: The filter cake was washed with water and dried to obtain 0.46 g of a light yellow ellagic acid product with a content of 98.8%.

[0033] The structural formula of ellagic acid is as follows: The HPLC chromatogram obtained in this embodiment, 1 H-NMR spectrum and 13 C-NMR spectrum is shown in Figure 2 to Figure 4 .

[0034] Example 3

[0035] The method for preparing ellagic acid by using tannin of physalis, comprises the following specific steps:

[0036] (1) Hydrolysis: Take 5 g of caryophyllaceous tannin, dissolve it in 100 mL of warm water, add 1 g of mpg-C3N4 photocatalyst, and stir the reaction at 80°C for 1.5 h.

[0037] (2) Acidification separation: Add dilute hydrochloric acid to the reaction solution while stirring until the pH value of the reaction solution reaches 5, filter, wash the filter cake with water, and dry to obtain 1.59 g of crude ellagic acid product, the purity of which is 66.8% as determined by HPLC, with a yield of 31.8%.

[0038] (3) Refining and purification: The crude ellagic acid product is added to a sodium hydroxide solution and activated carbon, and reacted at 50°C for 1 hour. The reaction solution is filtered, and the filter cake is washed with water. The filtrate and the washing solution are combined, and dilute hydrochloric acid is added dropwise to adjust the pH value of the solution to 4. The light yellow ellagic acid refined product is filtered to obtain.

[0039] (4) Drying: The filter cake was washed with water and dried to obtain 0.5 g of a light yellow ellagic acid product with a content of 99.8%.

[0040] Example 4

[0041] The method for preparing ellagic acid by using tannin of physalis, comprises the following specific steps:

[0042] (1) Hydrolysis: Take 5 g of caryophyllaceous tannin, dissolve it in 100 mL of warm water, add 1.5 g of mpg-C3N4 photocatalyst, and stir the reaction at 100°C for 30 min.

[0043] (2) Acidification separation: Add dilute hydrochloric acid to the reaction solution obtained in step 2 while stirring until the pH value of the reaction solution reaches 5, filter, wash the filter cake with water, and dry to obtain 1.67 g of crude ellagic acid product, the purity of which is 64.7% as determined by HPLC, with a yield of 33.4%.

[0044] (3) Refining and purification: The crude ellagic acid product is added to a sodium hydroxide solution and activated carbon, and reacted at 50°C for 1 hour. The reaction solution is filtered and the filter cake is washed with water. The filtrate and the washing solution are combined, and dilute hydrochloric acid is added dropwise to adjust the pH value of the solution to 4. The light yellow ellagic acid refined product and the refined filtrate are filtered to obtain.

[0045] (4) Drying: The filter cake was washed with water and dried to obtain 0.6 g of a light yellow ellagic acid product with a content of 98.8%.

[0046] Example 5

[0047] The method for preparing ellagic acid by using tannin of physalis, comprises the following specific steps:

[0048] (1) Hydrolysis: Take 5 g of caryophyllaceous tannin and dissolve it in 100 mL of the refined filtrate in Example 4. Add 1.5 g of mpg-C3N4 photocatalyst and stir the reaction at 100°C for 30 min.

[0049] (2) Acidification separation: Add dilute hydrochloric acid to the reaction solution obtained in step 2 while stirring until the pH value of the reaction solution reaches 5, filter, wash the filter cake with water, and dry to obtain 1.72 g of crude ellagic acid product, the purity of which is 63.5% as determined by HPLC, and the yield is 34.4%.

[0050] (3) Refining and purification: The crude ellagic acid product is added to a sodium hydroxide solution and activated carbon, and reacted at 50°C for 1 hour. The reaction solution is filtered, and the filter cake is washed with water. The filtrate and the washing solution are combined, and dilute hydrochloric acid is added dropwise to adjust the pH value of the solution to 4. The light yellow ellagic acid refined product is filtered to obtain.

[0051] (4) Drying: The filter cake was washed with water and dried to obtain 0.61 g of a light yellow ellagic acid product with a content of 98.6%.

[0052] Embodiment 6:

[0053] Preparation of Oak Tannin

[0054] The rubber bowl is crushed and heated and extracted with water as a solvent. The extraction method can be conventional immersion, microwave-assisted extraction, and ultrasonic-assisted extraction. The extraction times are 1-3 times, and the extraction time of each time is 1-3 hours. The residue is filtered out, vacuum-heated, concentrated, and dried to obtain the rubber bowl tannin.

[0055] Example 7

[0056] The method for preparing ellagic acid by using oak tannin comprises the following specific steps:

[0057] (1) Hydrolysis: Take 5 g of oak tannin, dissolve it in 100 mL of warm water, add 0.5 g of mpg-C3N4 photocatalyst, and stir the reaction at 60°C for 1.0 h.

[0058] (2) Acidification separation: Add dilute hydrochloric acid to the reaction solution while stirring until the pH value of the reaction solution reaches 6, filter, wash the filter cake with water, and dry to obtain 1.64 g of crude ellagic acid product, the purity of which is 68% as determined by HPLC, with a yield of 32.8%.

[0059] (3) Refining and purification: Add the crude ellagic acid product to a sodium hydroxide solution and activated carbon, react at 50°C for 1 hour, filter the reaction solution, wash the filter cake with water, and combine the filtrate and washing solution; add dilute hydrochloric acid to adjust the pH value of the solution to 4, and filter to obtain a light yellow ellagic acid refined product.

[0060] (4) Drying: The filter cake was washed with water and dried to obtain 0.52 g of a light yellow ellagic acid product with a content of 98.1%.

[0061] Example 8

[0062] The method for preparing ellagic acid by using oak tannin comprises the following specific steps:

[0063] (1) Hydrolysis: Take 5 g of rubber tannin, dissolve it in 100 mL of warm water, add 1 g of mpg-C3N4 photocatalyst, and stir the reaction at 80°C for 0.5 h.

[0064] (2) Acidification separation: Add dilute hydrochloric acid to the reaction solution while stirring until the pH value of the reaction solution reaches 5, filter, wash the filter cake with water, and dry to obtain 1.67 g of crude ellagic acid product, the purity of which is 68.8% as determined by HPLC, with a yield of 33.4%.

[0065] (3) Refining and purification: The crude ellagic acid product is added to a sodium hydroxide solution and activated carbon, and reacted at 50°C for 1 hour. The reaction solution is filtered, and the filter cake is washed with water. The filtrate and the washing solution are combined, and dilute hydrochloric acid is added dropwise to adjust the pH value of the solution to 4. The light yellow ellagic acid refined product is filtered to obtain.

[0066] (4) Drying: The filter cake was washed with water and dried to obtain 0.5 g of a light yellow ellagic acid product with a content of 98.8%.

[0067] Example 9

[0068] The method for preparing ellagic acid by using oak tannin comprises the following specific steps:

[0069] (1) Hydrolysis: Take 5 g of oak tannin, dissolve it in 100 mL of warm water, add 1.5 g of mpg-C3N4 photocatalyst, and stir the reaction at 100 °C for 0.5 h.

[0070] (2) Acidification separation: Add dilute hydrochloric acid to the reaction solution obtained in step 2 while stirring until the pH value of the reaction solution reaches 5, filter, wash the filter cake with water, and dry to obtain 1.77 g of crude ellagic acid product, the purity of which is 68.7% as determined by HPLC, with a yield of 35.4%.

[0071] (3) Refining and purification: The crude ellagic acid product is added to a sodium hydroxide solution and activated carbon, and reacted at 50°C for 1 hour. The reaction solution is filtered and the filter cake is washed with water. The filtrate and the washing solution are combined, and dilute hydrochloric acid is added dropwise to adjust the pH value of the solution to 4. The light yellow ellagic acid refined product and the refined filtrate are filtered to obtain.

[0072] (4) Drying: The filter cake was washed with water and dried to obtain 0.6 g of a light yellow ellagic acid product with a content of 98.8%.

[0073] Example 10

[0074] The method for preparing ellagic acid by using oak tannin comprises the following specific steps:

[0075] (1) Hydrolysis: 5 g of oak tannin was dissolved in 100 mL of the refined filtrate obtained in Example 9, and 1.5 g of mpg-C3N4 photocatalyst was added. The mixture was stirred at 100° C. for 0.5 h.

[0076] (2) Acidification separation: Add dilute hydrochloric acid to the reaction solution obtained in step 2 while stirring until the pH value of the reaction solution reaches 5, filter, wash the filter cake with water, and dry to obtain 1.85 g of crude ellagic acid product, the purity of which is 68.3% as determined by HPLC, with a yield of 37.0%.

[0077] (3) Refining and purification: The crude ellagic acid product is added to a sodium hydroxide solution and activated carbon, and reacted at 50°C for 1 hour. The reaction solution is filtered, and the filter cake is washed with water. The filtrate and the washing solution are combined, and dilute hydrochloric acid is added dropwise to adjust the pH value of the solution to 4. The light yellow ellagic acid refined product is filtered to obtain.

[0078] (4) Drying: The filter cake was washed with water and dried to obtain 0.61 g of a light yellow ellagic acid product with a content of 98.5%.

[0079] Comparative Example 1: Based on Example 2, the only difference is that the mpg-C3N4 photocatalyst was not added in step (1). Other reaction conditions and experimental operations were the same. As a result, no ellagic acid product was obtained.

[0080] Comparative Example 2: Based on Example 2, the only difference is that the photocatalyst added in step (1) is NiCo-MOFs (the catalyst can photocatalyze the degradation of lignin to prepare high value-added small molecule polyphenol compounds, and the relevant results are published in: Zhou et al., Spherical NiCo-MOFs catalytic hydrogenolysis of lignin dimers and enzymatic lignin to value-added liquid fuels under nitrogen atmosphere. Fuel, 2022, 315, 123156; Zhou et al., Ni-based MOFs catalytic oxidative cleavage of lignin models and lignosulfonate under oxygen atmosphere. Fuel, 2022, 320, 123993). Other reaction conditions and experimental operations are the same. As a result, no ellagic acid product was obtained.

[0081] It can be seen from the above comparative examples that the mpg-C3N4 photocatalyst in the present invention has catalytic selectivity, which is the key to the present invention.

[0082] The above embodiments and comparative examples are only for the purpose of clear demonstration, and are not limited to the above embodiments. For those skilled in the art, the above embodiments have many variations or combinations, and it is not necessary and impossible to cite all the embodiments here. Therefore, the variations or changes made based on the above embodiments are still within the protection scope of the present invention.

Claims

1. A method for preparing ellagic acid by photocatalytic tannin, characterized in that: The following steps are involved: S1, dissolving tannin in water, then adding photocatalyst mpg-C3N4 to carry out photocatalytic degradation reaction, adding acid to carry out acidification precipitation after the reaction, filtering, washing and drying the filter cake to obtain crude ellagic acid; S2. The crude product is dissolved with alkali, then decolorized, and then acid is added to reduce the precipitate, which is filtered, washed, and dried to obtain the ellagic acid product.

2. The method according to claim 1, characterized in that: The tannin is oak tannin and / or caraway tannin.

3. The method according to claim 1, characterized in that: The mass ratio of the tannin to water is 1:10-40.

4. The method according to claim 1, characterized in that: The amount of photocatalyst added is 10~20% of the mass of tannin.

5. The method according to claim 1, characterized in that: The reaction temperature in S1 is 60-100°C, and the reaction time is 0.5-1.5h.

6. The method according to claim 1, characterized in that: The acid added in S1 is hydrochloric acid solution, and the pH is adjusted to below 6.

7. The method according to claim 1, characterized in that: The crude product in S2 is dissolved with sodium hydroxide solution, activated carbon is added for decolorization, and then the activated carbon is removed.

8. The method according to claim 1, characterized in that: The acid in S2 is hydrochloric acid solution, and the pH is adjusted to below 4.

9. Application of mpg-C3N4 as photocatalyst in the preparation of ellagic acid from plant tannins.

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